erstwhile vs sometime

erstwhile

adj
  • Former, previous. 

  • Respected, honourable. 

sometime

adj
  • Former, erstwhile; at some previous time. 

  • Occasional. 

adv
  • At an indefinite but stated time in the past or future. 

How often have the words erstwhile and sometime occurred in a corpus of books? (source: Google Ngram Viewer )